Permian and Triassic Paleogeography of the Eastern Klamath Arc and Eastern Hayfork Subduction Complex, Klamath Mountains, California: Evidence from Lithotectonic Associations and Detrital Zircon

MILLER, M. MEGHAN, and JASON B. SALEEBY, California Institute of Technology, Pasadena, CA

Middle Permian and Middle Triassic volcanic-hypabyssal intrusive complexes form ensimatic arc deposits in the eastern Klamath terrane. Sedimentary matrix melange with blocks of sandstone, chert, and Tethyan fauna-bearing limestone compose the westward-lying eastern Hayfork terrane. Limestone olistoliths were derived from seamounts and incorporated into a subduction complex that was active during the Late Triassic and perhaps as early as the Permian. Geologic and biogeographic relations have previously been interpreted to imply a genetic relation between an ensimatic arc and subduction complex, constraining Permian(?)-Triassic subduction as eastward dipping.

Quartzarenite from the melange matrix was derived from a mature continental source and yielded detrital zircon for isotopic provenance study. Homogeneous dark pink to ruby red, very well-rounded zircons confirm well-mixed continental provenance, and were difficult to subdivide into color and morphology fractions of possible age significance. Nevertheless, nine multi-grain fractions were sorted and some dispersion of ages was achieved. 207Pb/206Pb ages cluster between 2.046 and 2.139 Ga, and generally correlate to slight changes in color. Such ages suggest, but do not require, a North American source. Based on quartz and zircon provenance, neither the zircon nor the quartz arenite was directly derived from older units in the Klamath Mountains. These data imply that the trench intersect d a continental source along strike, and quartz sands were transported longitudinally within the trench.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)